Day of Year Calculator
Part of Time & Date Calculators
Find which day of the year any date falls on. Convert dates to ordinal day numbers from 1 to 366.
What is Day of Year?
The day of year, also known as ordinal date or Julian day, is a simple calendar system that represents dates as the number of days since the beginning of the year. January 1st is day 1, January 2nd is day 2, and so on through December 31st, which is day 365 (or 366 in leap years).
How to Use This Calculator
Select any date using the date picker, or click "Today" to use the current date. Click "Calculate" to see the day number along with additional information including day of week, week number, quarter, and how many days remain in the year.
Common Uses for Day of Year
Agriculture and Farming: Farmers use ordinal dates to track planting schedules, growing seasons, and harvest times. Agricultural almanacs often reference crop events by day of year.
Scientific Research: Researchers use day of year for consistent date representation across different calendar systems, especially in climate studies, environmental monitoring, and astronomical observations.
Programming and Data Analysis: Many programming languages and databases support ordinal date formats for efficient date calculations and comparisons.
Project Management: Day of year helps calculate project timelines and track progress through annual cycles. Use our Week Number Calculator for ISO week-based tracking.
Calculating Day of Year
The day of year is calculated by counting all days from January 1st up to and including the target date. For leap years, February 29th is day 60, and all subsequent dates are shifted by one day compared to non-leap years. The calculation must account for the varying lengths of months and whether the year is a leap year.
Leap Years and Day Numbers
In leap years, the maximum day number is 366 instead of 365. This affects all dates after February 28th. For example, March 1st is day 60 in non-leap years but day 61 in leap years. Our calculator automatically handles leap year adjustments to give you accurate results. Use our Leap Year Calculator to check any year.
Week Numbers Explained
The ISO week date system assigns a week number to each week of the year. Week 1 is the first week containing a Thursday, which is usually the week with January 4th. This system ensures that each year has either 52 or 53 complete weeks, with weeks starting on Monday. For detailed date arithmetic, use our Date Calculator.